A quantitative immunofluorescence test for the detection of anti-Candida antibodies

Characterization of specific anti-Candida IgM, IgA and IgE: diagnostic value in deep-seated infections

The proposed serological diagnosis of systemic Candida infections is based on a microplate immunocapture technique detecting IgM, IgA and IgE anti-Candida antibodies. Activity is revealed with a suspension of human erythrocytes sensitized with somatic antigen of Candida albicans, and is quantified on an automated plate reader. The sera were obtained from patients with deep-seated (n = 56) and superficial (n = 193) candidosis. We compared this immunological method with a combination of indirect immunofluorescence and co-immunoelectrodiffusion. The immunocapture method was more sensitive (80.4% vs. 48.2% with indirect immunofluorescence and 58.9% with co-immunoelectrodiffusion), and often provided the diagnosis at an earlier stage, with clear therapeutic advantages. The IgA isotype was a particularly valuable marker of deep-seated Candida infections.

Enzyme immunoassays for invasive Candida infections: reactivity of somatic antigens of Candida albicans

The main problem encountered with serodiagnostic tests for Candida infections is their failure to differentiate between invasive and superficial candidosis. Recent immunoblotting studies suggested that the use of selective somatic proteins of Candida albicans as antigens might be a promising approach toward developing a new generation of serodiagnostic assays. In this study major cytoplasmic protein antigens with molecular weights of 47,000 (47K), 46,000 (46K), 45,000 (45K), and 29,000 (29K) were identified as potential marker antigens for antibody detection in invasive candidosis. Continuous-flow isoelectric focusing was employed to enrich the proteins in two fractions, one of them containing the 47K and 29K proteins and the other one containing predominantly the 47K and 45K major proteins. These antigens and a whole somatic antigen extract were used to establish enzyme immunoassays (EIAs) for antibody detection. Whereas all tests were able to discriminate between patients with invasive candidosis (n = 27) and normal healthy volunteers (n = 167), as proved by graphic marker analysis, the selective antigen EIAs were highly superior to the whole somatic antigen EIA and two serological standard assays (indirect immunofluorescence assay and indirect hemagglutination assay) when a panel of sera from patients with superficial candidosis (n = 34) was used as a negative control group. The use of the 47K-29K antigen fraction allowed the best differentiation between invasive and noninvasive candidosis. The corresponding immunoglobulin G class-specific EIA had a sensitivity of 81.5% and a specificity of 97% for both negative control groups as well.

Detection of serum antibody to Brucella abortus in cattle by use of a quantitative fluorometric immunoassay

A quantitative fluorometric immunoassay (FIAX) was adapted for the detection of serum antibodies to Brucella abortus in cattle. Results are expressed in nanograms of immunoglobulin binding the antigen carrier. The FIAX was compared with the standard tube agglutination, Rivanol precipitation, and complement fixation tests, using 285 serum samples from vaccinated, challenged, or control cattle. Linear regression analysis indicated a significant correlation among all four serological tests; the FIAX test correlated best with the Rivanol test. Ninety sera were from vaccinated and nonvaccinated cattle that were challenged with virulent B. abortus 2308. The sensitivity and specificity of each serological test were determined based on culture results from these cattle. The FIAX was the most sensitive of the four serological tests, detecting 79.2% of the culture-positive animals. The FIAX was the least specific, with 15.4% of the culture-negative animals being classified as positive. Eighty-eight sera were from cattle vaccinated with strain 19 but not challenged. All four serological tests had a statistically significant ability to distinguish sera from control and vaccinates on the basis of mean titers. The mean titer of vaccinates was also significantly different from that of challenged animals. Advantages and disadvantages of the FIAX test for bovine brucellosis are discussed.

A purified polysaccharide isolated from Candida albicans induces antibody response in vitro by human peripheral blood lymphocytes and discriminates between sera from normal and Candida albicans-infected individuals

A purified polysaccharide extracted from Candida albicans (MPPS), stimulates in vitro synthesis of specific antibodies by human peripheral blood lymphocytes. These antibodies can be detected by a sensitive enzyme-linked immunoassay. The same assay can be applied to the quantitation of anti-candida antibodies in serum. Statistically significant differences were found between sera of normal and candida-infected individuals.

Identification and molecular weight characterization of antigens from Candida albicans that are recognized by human sera

Antigenic components in the cytoplasmic extract of Candida albicans were examined after fractionation by concanavalin A-Sepharose and DEAE-Sephacel ion-exchange chromatography. Fractions from the DEAE column were tested by fused rocket immunoelectrophoresis for their reactivity with antibodies in the sera of 20 patients with disseminated candidiasis. Three groups of fractions (regions A, B, and C) from the DEAE column were defined by their reactivity with these sera. Immunoblot analysis with 20 human sera identified 18 antigenic components in regions A, B, and C. Region A contained nine antigens, region B contained four antigens, and region C contained five antigens. Region A contained an antigen with an apparent molecular weight of 48,000 that was recognized by 7 of 10 sera from patients with disseminated candidiasis. Immunoprecipitation experiments with labeled proteins from region A and 51 human sera also demonstrated the presence of a major antigen whose apparent molecular weight is 48,000 to 52,000. The 48- to 52-kilodalton protein is an abundant protein in region A and is the most frequently recognized protein by antibodies in the sera of patients with disseminated candidiasis. Patients with disseminated candidiasis had significantly higher levels of antibody (immunoglobulin G) (P less than 0.001) directed against the 48- to 52-kilodalton protein than did patients with noninvasive forms of candidiasis, patients with other fungal infections, or normal, healthy persons.

A fluorescein-linked immunoabsorbent assay for the detection of antibacterial antibodies in secretions and serum

A rapid, quantitative solid-phase immunofluorescence assay has been developed to measure antibodies reactive with Streptococcus mutans in saliva and serum. Formalin killed bacteria were adsorbed to cellulose acetate discs and antibodies bound to the antigen-coated immunoabsorbent were detected by use of fluorescein-labeled antibody to human immunoglobulin isotypes. Quantitation was performed by placing the immunoabsorbent discs in a fluorometer. Low levels of naturally occurring antibodies reactive with S. mutans were easily detected in saliva and serum from normal human subjects.

Detection of antibodies to Legionella pneumophila in immune guinea pig serum by solid-phase immunofluorescence

A semiautomated solid-phase immunofluorescence apparatus (FIAX; International Diagnostic Technology, Santa Clara, Calif.) was utilized to develop a rapid method for detection of antibody to Legionella pneumophila. The sera from guinea pigs immunized with a mixture of killed L. pneumophila and Freund complete adjuvant displayed markedly enhanced antibody activity as measured by FIAX when compared with that obtained from adjuvant-injected or unimmunized animals. A correlation was observed between FIAX net fluorescence units and microagglutination titers of serum samples obtained from immunized animals. Within-run and between-run coefficients of variation performed on selected immune serum samples were low. These results demonstrated that the FIAX method could readily and reproducibly detect Legionella-specific antibodies in the sera of actively immunized animals and suggest the possibility of a broader application of FIAX in the serological detection of exposure to L. pneumophila antigen.